In many situations, it is desirable to separate a slurry of raw material into constituent solid and liquid components. For example, while the general composition of municipal waste may be known, any particular gallon of municipal waste may contain a variety of unknown solid or liquid components. Before municipal waste can be introduced into the environment, it is typically processed to remove at least a portion of the liquid or solid components thereof. Municipal waste is thus typically processed in a variety of stages designed to remove liquid and solid materials that might be unsuitable for discharge into the environment.
Modern animal husbandry operations such as dairy farms represent another example of a system in which the processing of a slurry of raw material to remove solid particulates is advantageous. The present invention is of particular significance in the context of processing waste from a dairy farm, and that application of the present invention will be described in detail herein. However, the principles of the present invention may be applied to any system in which a slurry of raw material is processed to remove solid components from the slurry.
Dairy farms often require the handling of relatively large numbers of animals in indoor facilities. For example, cows in a dairy operation are kept at least part of the day in stalls defining a stall resting surface. The stall resting surface should be covered with bedding material that is comfortable to lie on, provides uniform support, is cool in the summer, is non-abrasive, and provides confident footing during reclining and rising maneuvers. From the perspective of the operator of the dairy facility, bedding material should not be detrimental to the health of the cows or the quality of the milk produced by the cows. Sand has been proven to be advantageous as a bedding material and is commonly used in modern dairy operations.
When sand is used as a bedding material, the sand often becomes mixed with manure and other materials that collect within a dairy facility. When cleaning systems are used to remove manure from the diary facility, raw slurry material is formed containing rinse liquids, liquid manure, solid manure, relatively heavy solids such as sand, relatively light solids such as fibers and/or corn, and possibly other contaminants. The term “relatively heavy” is used herein to refer to a material with a density greater than that of water, while the term “relatively lighter” is used herein to refer to a material with a density less than that of water.
When possible, it is desirable to convert components of the raw slurry mixture to usable materials and/or reuse the components of the raw slurry mixture. In the context of a dairy facility, sand used as bedding material represents a cost. To reuse the sand as bedding material, the sand must be clean. On the other hand, if manure and other digestible materials are to be converted to energy using an anaerobic digester, removal of non-digestible materials such as sand allows the anaerobic digester to operate more efficiently.
In addition, certain separation systems are highly effective at removing large amounts of relatively heavy particulate such as sand from a raw slurry. However, these separation systems employ a substantial amount turbulence that tends to cause smaller particulates (fine sand) to be suspended within rinse water. Accordingly, although a particulate material may be more dense than water, that relatively heavy particulate can carried with rinse water out of the separation system. Such relatively heavy particulate that is carried with rinse water out of a separation system will be said to have bypassed the separation system.
The present invention relates to the separation of raw slurry materials into its constituent components such as manure, waste and rinse liquids, relatively light (e.g., less dense than water) fiber components such as corn, and relatively heavy (e.g., more dense than water) non-digestible components such as sand. Removal of sand from the raw slurry material further forms a processed slurry (low sand content) that is more appropriate for further processing operations such as extraction of water, composting, and/or digesting.